Switchable multi-wavelength erbium-doped random distributed feedback fiber laser incorporating two-stage Sagnac filter

Abstract

A low-threshold and simple structure switchable multi-wavelength fiber laser based on random distributed feedback (RDFB) is presented. The experiment setup incorporates a two-stage Sagnac fiber loop mirror, an 8 m long erbium-doped fiber (EDF), and a 25 km long single-mode fiber (SMF). The SMF provides RDFB via Rayleigh scattering. Due to the implementation of the half-open cavity structure and the gain generated by the EDF, the laser threshold can be significantly suppressed to 60 mW, and the slope efficiency of output lasing power against pump power is ∼0.9%. By adjusting the polarization controllers of the proposed two-stage Sagnac loop mirror, single-, double-, triple-, and quadruple-wavelength lasing channels in the range of 1527–1534 nm are achieved. In the case of quadruple-wavelength channel lasing, the optical signal noise ratio is up to 33 dB under the 180 mW pump power. The proposed random fiber laser can be applied in distributed sensing systems and biomedical imaging.